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Fix write to closed channel panic() in internal/connection during connection close #539

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merged 2 commits into from
Jun 30, 2021
Merged

Fix write to closed channel panic() in internal/connection during connection close #539

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366a7b4
Fix panic() in internal/connection when writing to a closed channel d…
Jun 11, 2021
a1f2eca
merge master code and fix conflict
wolfstudy Jun 30, 2021
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30 changes: 26 additions & 4 deletions pulsar/internal/connection.go
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,7 @@ type connectionState int32
const (
connectionInit = iota
connectionReady
connectionClosing
connectionClosed
)

Expand All @@ -98,6 +99,8 @@ func (s connectionState) String() string {
return "Initializing"
case connectionReady:
return "Ready"
case connectionClosing:
return "Closing"
case connectionClosed:
return "Closed"
default:
Expand Down Expand Up @@ -142,6 +145,7 @@ type connection struct {

requestIDGenerator uint64

incomingRequestsWG sync.WaitGroup
incomingRequestsCh chan *request
incomingCmdCh chan *incomingCmd
closeCh chan interface{}
Expand Down Expand Up @@ -331,10 +335,15 @@ func (c *connection) waitUntilReady() error {
}

func (c *connection) failLeftRequestsWhenClose() {
// wait for outstanding incoming requests to complete before draining
// and closing the channel
c.incomingRequestsWG.Wait()
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I'm a little confused why are we waiting here?

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@cckellogg ,
At this point we are sure that the closeCh is closed and that the state of the connection is either connectionClosing or connectionClosed. We wait to be sure that there will be no further writes to the incomingRequestsCh before attempting to drain and close it. It is possible for the sending go-routine to be executing either of the following lines at the time this function is executed:

As mentioned in the motivation for this MR:

When two cases of a select are valid, the case executed is chosen at random; see https://tour.golang.org/concurrency/5

Whenever I see a channel being closed by a reader go-routine I am suspicious of writers attempting to write to the channel after it is closed.


reqLen := len(c.incomingRequestsCh)
for i := 0; i < reqLen; i++ {
c.internalSendRequest(<-c.incomingRequestsCh)
}

close(c.incomingRequestsCh)
}

Expand Down Expand Up @@ -546,8 +555,13 @@ func (c *connection) Write(data Buffer) {

func (c *connection) SendRequest(requestID uint64, req *pb.BaseCommand,
callback func(command *pb.BaseCommand, err error)) {
if c.getState() == connectionClosed {
c.incomingRequestsWG.Add(1)
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Why is this waitgroup needed for both send requests?

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As mentioned #539 (comment) we need to track all writes to the incomingRequestsCh

defer c.incomingRequestsWG.Done()

state := c.getState()
if state == connectionClosed || state == connectionClosing {
callback(req, ErrConnectionClosed)

} else {
select {
case <-c.closeCh:
Expand All @@ -563,7 +577,11 @@ func (c *connection) SendRequest(requestID uint64, req *pb.BaseCommand,
}

func (c *connection) SendRequestNoWait(req *pb.BaseCommand) error {
if c.getState() == connectionClosed {
c.incomingRequestsWG.Add(1)
defer c.incomingRequestsWG.Done()

state := c.getState()
if state == connectionClosed || state == connectionClosing {
return ErrConnectionClosed
}

Expand All @@ -586,7 +604,8 @@ func (c *connection) internalSendRequest(req *request) {
c.pendingReqs[*req.id] = req
}
c.pendingLock.Unlock()
if c.getState() == connectionClosed {
state := c.getState()
if state == connectionClosed || state == connectionClosing {
c.log.Warnf("internalSendRequest failed for connectionClosed")
if req.callback != nil {
req.callback(req.cmd, ErrConnectionClosed)
Expand Down Expand Up @@ -755,6 +774,8 @@ func (c *connection) UnregisterListener(id uint64) {
// broadcasting the notification on the close channel
func (c *connection) TriggerClose() {
c.closeOnce.Do(func() {
c.setState(connectionClosing)

cnx := c.cnx
if cnx != nil {
cnx.Close()
Expand All @@ -775,9 +796,10 @@ func (c *connection) Close() {
}

c.log.Info("Connection closed")
c.TriggerClose()
// do not use changeState() since they share the same lock
c.setState(connectionClosed)
c.TriggerClose()

c.pingTicker.Stop()
c.pingCheckTicker.Stop()

Expand Down